Method of protecting ferrous metal surfaces from rerusting



United States Patent 3 135 632 METHOD or rno'rlicrilso rnnnons METALSURFAE FROM RERUSTING William R. Lucas, Huntsville, Ala., and Karl F.Eager,

Clear-field, Pa, assignors to the United States of Amerion asrepresented by the Secretary of the Army No Drawing. Filed May 24, 1957,Ser. No. 661,548

8 Claims. (Cl. 134-28) (Granted under Title 35, U.. Code (1952), sec.266) 10 The invention described herein may be manufactured and used byor for the Government for governmental purposes, without the payment tous of any royalties thereon.

This invention relates to the protection of ferrous metal surfacesagainst rerusting. In particular, it is directed to a new and improvedmethod for the prevention of the rerusting which normally occurs uponthe removal of freshly pickled carbon or low alloy ferrous metals from apickling bath by the addition of acridine, certain substituted acridinesand mixtures thereof to the picking acid bath.

It is well known that after various mill operations and at numerousstages in the fabrication of finished products, for instance, forgalvanizing, tinning, electroplating and painting, it is necessary toremove oxides and other scales from various metal surfaces. Commerciallyfor carbon or low alloy ferrous metals, this is done by the processcalled pickling wherein the ferrous metals being treated are immersed inacid solutions. Various acids are used in commercial pickling, such assulfuric, hydrochloric and phosphoric acids. Because of its relativecommercial availability, sulfuric acid is more widely used than allothers.

It is also known that in order to reduce the attack of the picklingacids on the base ferrous metal and thus to prevent the waste both ofthe acid and the metal, additives termed inhibitors are incorporatedinto the pickling baths. Many satisfactory commercial inhibitors existwhich accomplish this function of protecting the metal surfaces fromacid attack while the metal is immersed in the pickling bath.

To the knowledge of the inventors however, none of these inhibitors hadthe attribute of protecting the highly active, freshly pickled metalsurfaces from rerusting upon removal from the bath.

After the metal has been removed from the pickling bath, by knownmethods, portions of the thin residual film of pickling acid and salts,as well as portions of the inhibitor additive, are then rinsed from themetal. At this stage and in order to protect the metal surfaces while intemporary or semi-permanent storage from the rusting caused by exposureto the elements, i.e., the cf- .fects of atmospheric type oxidation, itis necessary to vide for the protection of the metal surface againstrerusting by the use of a substance which is non-oily.

A further obejction to this type of treatment arises as the result ofthe fact that the oily film must subsequently be removed by any of thewell-known methods when further use of the metal is desired.Accordingly, it is an additional object of the present invention toeliminate the operational necessity for removal of a rust protectivecoating when further use of the ferrous metal is desired.

It can then be seen that the elimination of these repetitive coating andremoval operations during the processing of the metal would expedite andsimplify overall production-line type fabrication processes. It is afurther object of this invention to provide a method to expedite andsimplify the overall fabrication process by the elimination of thecoating, coating removal and recoating operations.

According to our method, once the pickling bath oporation has beencompleted the freshly pickled metal may be simply allowed to dry or,alternately, rinsed in water and then allowed to dry. Accordingly, it isa still further object of the present invention to provide a methodwhereby freshly pickled ferrous metal surfaces are rendered resistant torerusting. Other objects will in part be apparent and will in partappear hereinafter.

Unexpectedly it was found that the addition to the pickling bath of asmall amount of acridine, l-amino acridine, l-bromo-acridine or mixturesthereof, either alone or in combination with other inhibitors, wouldresult in rendering the highly active, freshly pickled metal resistantto rerusting upon exposure to atmospheric or other elemental effects.Acridine is a benzolog of quinoline having a structural formulacorresponding to:

Relatively, acridine appears to afford more protection than thesubstituted acridines mentioned, as will more fully appear from thefollowing examples.

It can be seen that by this new and novel method the coating,coating-removal and recoating operational steps of presently availablemethods can be entirely eliminated from pickling bath procedures.Furthermore, the use of this new and novel method wherein the moreeffective inhibitors are also incorporated in the pickling bath willtend to give the optimum for not only the protection from pickling acidaction on the ferrous metals, but after-rust protection as well.

It has been our experience that samples of ferrous metals removed frompicking baths, if not otherwise treated, will be almost completelycovered with rust within 24 hours. Samples of steel surfaces pickled ina solution contaniing acridine, an additional inhibitor and sulfuricacid have been exposed to ambient laboratory temperatures for severalmonths without the slightest evidence of rust.

This peculiar property of acridine, l-amino-acridine, l-bromo acridineand mixtures thereof could not be de duced from either test comparisonswith other substituted acridines or from comparisons with other relatedheterocyclic compounds, for instance, acridone, quinoline, pyridine orB-naphthoquinoline. Although some of these compounds are acid attackinhibitors, as shown in our copending application, Serial No. 668,283,filed January 25, 1957, now US. Patent 2,981,617, they afford, as willbe indicated by the test data contained in the examples hereafter setforth, no protection to the metal against rerusting after pickling.

Thus the value of this invention can be appreciated when it isconsidered that, by the addition of a small amount of acridine, l-aminoacridine, l-bromo-acridine, and mixtures thereof to the pickling bath,the necessity for immediate rust prevention treatment of the metalfollowing pickling is eliminated. Furthermore, without any additionaltreatment, ferrous metals thus protected may be primed and painted atany time up to one year after pickling. V

The following examples are given by way of illustration only and are notintended to limit the scope of this invention in any way:

The hydrogen evolution method was employed to determine the percentageretardation (inhibition) in each of the following examples. This methodconsists of immersing the metal samples in a gas burette filled with thepickling acid under consideration. Below this specimen, a small orificeleads to the overflow tube so that the system is at atmosphericpressure, and the rate of attack of the acid upon the metal could befollowed by reading the volume of hydrogen evolved. An inhibited acidtest is always compared with an uninhibited acid test for controlpurposes, and the percentage retardation is calculated as follows:

Percent retardation volume of H2 uninhibited X The employment of thismethod makes it possible to obtain data at very frequent intervals whichis not feasible when using the weight-loss method. The sample immersionshereinafter described were continued for 24 hours; the specimens werethen removed from the bath; rinsed with Water and placed on a rack todry. Within 24 hours after being placed on the drying rack, the metalsamples were examined to determine the extent of the protection againstrerusting. This determination was made by measuring the percentage ofsurface covered by rust. In all cases, the samples of uninhibited metalswere found to be almost completely covered by rust within one hour.

EXAMPLE I Table I contains the results of tests which indicate the typeof inhibition and after-rust protection afforded by acridine when testedalone. Samples of SAE 1010 steel were cut to give a surface area of 37cm. and were ground to a smooth surface. After degreasing, therspecimens were placed in different gas burettes completely filled with l-Nsulfuric acid. The resultsof the tests in which acridine alone was addedto the acid are shown in Table I:

Table I AFTER RUST OF SAE 1010 STEEL WHEN PICKLED IN SUL- FURIC ACID TOWHICH ACRIDINE WAS ADDED tested for the different concentrations byweight percent of the acridine.

EXAMPLE II Table II involves a comparison of the protective effectafforded by acridine, l-amino acridine and l-bromo acridine as well as acomparison of the effectiveness of acridine, l-bromo acridine and1-amino acridine with respect to the ineffectiveness of the othersubstituted acridines tested.

Tests were performed under the same conditions and in the same manner asin Example I except that varying concentrations by weight percent of theacridine and substituted acridines were used. This table illustratesboth the retardation effectiveness and the after-rust protectionafforded by the various concentrations of acridine, 1- bromo acridineand l-amino acridine.

Table II IIiPlII IBITION AND AFTER RUST PROTECTION FROM THE TACK OF 1-NSULFURIC ACID ON MILD STEEL BY ACRIDINE AND SUBSTITUTED ACRIDINESOoncen- Retar- After-pick- Samples tration, dation, ling rust weightpercent protection,

percent percent Acridinc 0. 1 57 100 D 0. 05 67 100 0. 025 62 100 0. 169 90 0. 05 62 90 0. 025 62 90 O. 05 77 100 0. 025 -76 80 0. 1 92 0 0.05 90 p o 0. 025 0 0. 1 7o 0 O. 05 .74 0 0. 025 71 0 0. l 81 0 O. 05 860 0. 025 79 0 EXAMPLE III parison with that of the particular acidsolution to which acridine had been added.

Table III AFTER RUST PROTECTION OF ME 1010 STEEL WHEN PICKLgD IN VARIOUSACIDS TO wrnon ACRIDINE WAS ADDE Concen- Concen- After rust Acid tratlonof tration of protection,

acid noracridine percent mality l-N nil 0 2-N nil O 5-N nil 0 l-N 0.05100 2-N 0. 05 mo 5-N' 0.05 90 1-N nil 0 l-N 0.1 l-N 0.05 100 I-N 0.025100 l-N nil 0 l-N 0. i 100 .1-N 0.05 100 l-N 0. 025 100 D EXAMPLE IVTests were conducted under the same conditions and in the same manner asin Example I. However, other inhibitors were added to the acid solutionalong with the acridine for the purpose of illustrating that a moreeffective combined inhibition-after-rust protection could be obtained bythe addition of a more effective inhibitor in combination with theacridine. The compounds used were inhibitors of acid attack, but which,of themselves, afforded no protection against rerusting.

Table IV AFTER RUST OF SAE 1010 STEEL WHEN PIOKLED IN IN HIBIIEDSULFURIO ACID TO WEICH AGRIDINE WAS EXAMPLE V To illustrate thatmixtures of acridine and the specified substituted acridines were aseifective when mixed together as when used alone, tests were conductedunder similar conditions and in the same manner as in Example I exceptthat both SAE 1010 and SAE 4130 steels were tested. A mixture of 0.05%acridine and 0.025 l-bromo acridine resulted in a 100% after rustprotection for SAE 1010 steel. When tested with different samples of SAE1010 and SAE 4130 steel, a mixture of 0.05% acridine and 0.025% l-bromoacridine resulted in a 90% after rust protection in each case.

EXAMPLE VI To test the efiectiveness of acridine and l-bromo acridinewith low alloy steels, experiments were conducted in the same manner andunder similar conditions as those of Example I except that SAE 4130steel was used and 0.05 acridine added to l-N sulfuric acid. The resultsindicated an 80% after rust protection. 0.025% l-bromo acridine added toa l-N acid bath which contained a sample of SAE 4130 low alloy steelgave an 80% after rust protection.

EXAMPLE VII Although the tests listed in the previous examples ran 24hours, much less time is required for the reaction which affords theprotection against rerust. Tests were conducted in the same manner andunder the same conditions as discussed in Example I except thatspecimens were removed from the solution after short, graduated periodsof time, rinsed and allowed to air-dry. vThe specimens were examined forrust 24 hours after rinsing. The results of these tests are listed inTable V. I

6 Table V AFTER RUST OF SAE 1010 STEEL WHEN PICKLED IN l-N SULFURIO ACIDAcrldine, weight percent Length of pickle After rust protection, percent24 hours bon-ferrous metal surfaces, and low alloy ferrous metalsurfaces from rerusting after removal from acid pickling baths, thesteps which comprise: adding to the acid pickling bath a small amount ofan organic compound selected from the group consisting of acridine,l-amino acridine, l-bromo acridine and mixtures thereof, whereby themetal surfaces are rendered substantially inactive to the normal effectof atmospheric oxidation; removing the inactivated freshly pickled metalfrom the acid pickling bath; and allowing the metal to dry.

2. The method of claim 1 wherein the organic compound is an amountbetween .005 and .2% by weight acridine.

3. The method of claim 1 wherein the organic compound is an amountbetween .025 and .1% by weight 1- amino acridine.

4. The method of claim 1 wherein the organic compound is an amountbetween .025 and .1% by weight 1- bromo acridine.

5. The method of claim 1 wherein the organic compounnd is a mixture ofacridine and l-amino acridine.

6. The method of claim 1 wherein the organic compound is a mixture ofacridine and l-bromo acridine.

7. The method of claim 1 wherein the organic compound is a mixture ofl-amino acridine and l-bromo acridine.

8. In the method of protecting metal surfaces selected from the groupconsisting of ferrous metal surface, carhon-ferrous metal surfaces, andlow allow ferrous metal surfaces from rerusting after removal from acidpickling baths, the steps which comprise: adding to the acid picklingbath a small amount of an organic compound selected from the groupconsisting of acridine, l-amino acridine, l-bromo acridine and mixturesthereof, whereby the metal surfaces are rendered substantially inactiveto the normal effect of atmospheric oxidation; removing the inactivatedfreshly pickled metal from the acid pickling bath; rinsing the metalwith water; and allowing the metal to dry.

References Cited in the file of this patent UNITED STATES PATENTS1,503,443 Gravell July 29, 1924 1,678,775 Gravell July 31, 19282,037,762 Cole Apr. 21, 1936 2,814,593 Beiswanger Nov. 26, 1957

1. IN THE METHOD OF PROTECTING METAL SURFACES SELECTED FROM THE GROUPCONSISTING OF FERROUS METAL SURFACES, CARBON-FERROUS METAL SURFACES, ANDLOW ALLOY FERROUS METAL SURFACES FROM RERUSTING AFTER REMOVAL FROM ACIDPICKING BATHS, THE STEPS WHICH COMPRISE: ADDING TO THE ACID PICKLINGBATH A SMALL AAMOUNT OF AN ORGANIC COMPOUND SELECTED FROM THE GROUPCONSISTING OF ARCIDINE,1-AMINO ACRIDINE, 1-BROMO ACRIDINE AND MIXTURESTHEREOF, WHEREBY THE METAL SURFACES ARE RENDERED SUBSTANTIALLY INACTIVETO THE NORMAL EFFECT OF ATMOSPHERIC OXIDATION; REMOVING THE INACTIVATEDFRESHLY PICKED METAL FROM THE ACID PICKING BATH; AND ALLOWING THE METALTO DRY.